Spark gap arrangement for surge arresters



Filed Oct. 5. 1960 Jan. 8, 1933 w. MKCHLER ETAL 3,072,815

SPARK GAP ARRANGEMENT FOR SURGE ARRESTERS 4 Sheets-Sheet 1 INVENTORSWerner NdchLe h clhelm ZoLler P- IJJWEJOMM ATTORNEYS 8, 1963 w. MACHLERETAL Y 3,072,

SPARK GAP ARRANGEMENT FOR SURGE ARRESTERS Filed Oct. 5, 1960 4Sheets-Sheet 2 I 1 I I I i x i jfi ki gfim ATTORNEY .S

Jan. 8, 1963 ;w. MACHLER ETAL 3,072,815

SPARK GAP ARRANGEMENT FOR SURGE ARRESTERS 4 Sheets-Sheet Filed Oct. 5,1960 Werner N'achlr wL-zhem Z0146 .BY/P. J

I fwfmk Jan. 8, 1963 w. MKCHLER ETAL 3,072,815

SPARK GAP ARRANGEMENT FOR sum: ARRESTERS 4 Sheets-Sheet 4 Filed Oct. 5,1960 Werner NdchLer Wilhelm Z l BYP 02%., wk J A'fORNEYs ning, etc. Butdue to the reduced 7 Filed Oct. 5, 1960, Ser. No. 60,611

Claims priority, application Switzerland Oct. 6, 1959 5 Claims. (Cl.313-161) In connection with surge voltage arresters with a multiplespark gap and voltage-dependent resistors, increasingly lower sparkovervoltages and lower residual voltages are being demanded, correspondingto the different specifications in the various countries. But with. useof lower sparkover voltages it is possible to deal with over-voltagesoccurring in the circuit as well as voltages caused by lightratio ofsparkover voltage and the recovery voltage, the requirements, which thespark gaps have to meet with regard to the restrike voltage, alsoincrease. The protective level is reduced by the 'low residual voltage,which reduces the costs of the in- -sulation of the apparatus. The lowresidual voltage can be achieved, on the one hand, by improving thevoltage dependent resistors, and on the other hand, by reducing theamount of resistance. .;l 1igher'- follow-current. age. with agreater-follow-current naturally results in fresh But this must be paidfor by a The required higher restrike voltrequirements for the sparkgaps which the conventional plate-spark; gaps do not meet. As a suitablemeasure for increasing the extinguishing capacity of the spark gaps, .amethod where the'follow-current arc is allowed to migrate from itsorigin under the influence of a magnetic blast field is used to anincreasing extent. The blast field can be produced by causing thefollow-current to take a suitable course in the electrodes, or by blastcoils through which the follow-current flows, or by permanent magnets.Recently, the migration of the arc has been accompanied by an extensionof the arc. The resulting high voltage above the arc reduces thefollow-current and'thus relieves A the resistors. Thepresent inventionrelates to a spark gap arrange ment for surge arresters withvoltages-dependent resistors gandmagnetic blast field, where the sparkgaps consists of a number of axially stacked plates of insulationmaterial,

..which"are'provided'on each side with an electrode and -whereby ineachcase an electrode on one plate together with an electrode on anadjacent plate forms-a spark gap. With this spark gap arrangement it ispossible to extinguish several hundred amperes of follow-current with ahigh restrike voltage. At the same time, use is also made of the reliefof the resistors by an extension of the arc, The spark gaps should actin closedchambers, so that acompact arrangement is possible in thearrester insulator, without increasing the danger of a breakdown in theinterior of the insulator by are gases.

According to the invention the foregoing conditions are met in this way,that the two electrodes belonging to a plate extend from the center ofthe plate to the edge, and consist of one piece, which is inserted andfixed laterally in a slot of the plate, the entrance of the slot beingclosed by projections on the circumference of the adjacent plates aboveand underneath, and that the plates are provided with gas channels,which permit the circulation of gas from the arc of a spark gap throughthe plate to the sparkover distance of the spark gap above andunderneath.

The invention will be described more fully on the basis of theembodiments represented in the attached figures.

FIG. 1 is a schematic representation of an active ele- United StatesPatent different arrangement ment of a high voltage arrester withmagnetically blasted spark gaps.

FIG. 2 is a similar representation as FIG. 1, but with a of the blastcoils.

FIG. 3 shows an active element of the arrester with magnetically blastedspark gaps, partly in a section and partly in an elevation.

FIG. 4 is a top view of one of the insulating plates of the spark gap.

FIG. 5 is a section along the line V-V of FIG. 4.

FIG. 6 is a top view of an insulating plate of the spark gaps withbuilt-in electrodes.

FIG. 7 is a section along the line VII-VII of FIG. 6.

'FIGS. 8 and 9 are a top view and section respectively of one of theelectrode elements.

FIG. 10 shows a stack of spark gaps in the disassembled state. I

The active part of the surge arrester consists of the voltage-dependentresistors 1 and the stack of spark gaps 2 which are connected between ahigh voltage line 7 and the ground 8, as it can be seen from FIGS. 1-2.The resistors 1 have the function, as known, of limiting thefollow-current, while the spark gaps 2, interrupt the follow-current. Inorder to increase the quenching capacity of the spark gaps 2, thefollow-current arc in the spark gaps in blown away from its place oforigin by a magnetic field, the migration of the arc resulting at thesame time in an extension of the latter. The arc voltage thus achievedhelps to reduce the follow-current, so that the height of theresistancestack canbe reduced, which has a favorable effect on the residualvoltage. The blast field is produced on the one hand by a screw-shapedguidance of the current in the spark gaps, and on the other hand by theadditional blast coils 3, the two blast fields assisting each otherduring the entire extinguishing process.

The blast coils 3, can be arranged at both ends of the stack of sparkgaps 2, in series with the latter, as shown in FIG. 1, or they canextend as a unit around the entire stack of gaps (FIG. 2). Since theblast coils 3 have a relatively high inductivity, a nonlinear elementmust be connected in parallel to by-pass the surge-current with steepwave front. This can be a voltage-dependent resistor block, for example,also a resistor stack 1. In the present case, a spark gap 4, connectedin parallel to the blast coil 3 is used, which has the advantage,compared to the resistance block, that it produce no additional residualvoltage. This spark gap 4 can be built exactly like the extinguishingspark gap 2. For constructional reasons, however, a slightly modifiedform may be used, which will be described later. The spark gap 4 inparallel with the blast coil is also blasted magnetically, which has theadvantage that the arc in the spark gap 4, can be extinguished muchfaster, due to its migration and extension. The current rises thusfaster in the blast coil 3, which results in a rapid buildup of theblast field thus increasing the extinguishing effect.

The spark gap 2, consists of a number of identical spark gaps whoseconstruction can be seen from FIGS. 3 to 9. Each spark gap has a roundinsulating plate 5 which consists of pressable material and which has ahigh electric strength, a high creeping strength, good heat stabilityand high mechanical strength. The plate 5, is provided with a slot 6(FIG. 4), into which are inserted the two electrodes 24, made of onepiece and belonging to one plate. FIG. 6 shows the plate 5 withelectrodes 24 inserted, while FIGS. 8 and 9 respectively show the doubleelectrode 24 alone in an elevation and section respectively. To fastenthe electrodes 24, the plate 5 is provided on each side with a boss 23,which fits into the holes 9 provided in the electrodes. In the center ofthe plate 5 are provided, on both sides, depressions 10, which serve toincrease the creep path between the two electrodes of a 3 spark gap. Onthe electrodes 24 are attached metal tongues 22 (FIG. 6), which pressagainst the counterplate after the spark gaps have been assembled. Thesetongues 22 serve to pre-ionize the spark gaps.

The slot 6 widens toward the edge of the plate 5 in the opening 11. Thisopening is closed toward the outside by the bosses or projections 12 ofthe plates which lie above and underneath during the stacking, and issubdivided in the interior into two parts 20 and 21 (FIGS. 6 i

and 7). These bosses 12, serve at the same time to fix the insulatingplates 5, so that mutal turning is prevented. The plate 5 is providedwith an elevated edge 13, so that when the plates are assembled, sparkchambers 14 are formed which are closed toward the outside, and thestacked plates are secured at the same time against lateraldisplacement. Due to the wider elevations 15, gas channels are formed onthe plates (FIGS. 6 and 7).

The construction of the blast coils and of the respective spark gaps canbe seen from FIG. 3, which shows an arrester, partly in a section. Thevoltage-dependent resistors 1 and the above described stack of sparkgaps 2, are arranged in known manner in an insulator case 30. The blastcoil 3, provided at each end of the stack of spark gaps 2, is attachedon a coil form which consists of two parts 16 and 17, the plate-shapedpart being made preferably of the same heat-resistant insulatingmaterial as the plates 5 of the quenched spark gap 2. The spark gap 4,which is connected in parallel to the blast coil, is formed by anelectrode of the same form as that of the quenched spark gaps, and of acopper tube 18 which is embedded in the coil form 16, 17. This tube 18acts at the same time as a connection from the spark gap 4 to thecontact plate 19, which serves as an electric connection to the elementsbearing on the stack of spark gaps 2. The entire spark gap arrangementis under the action of the compression spring 3-1.

FIG. shows the various main parts of a stack of spark gaps correspondingto the arrangement in FIG. 1, in the order of their assembly, namely,from the top to the bottom, starting from the left, the upper blast coil3, the respective spark gap 4, the extinguishing spark gap 2, the lowerspark gap 4 and the lower blast coil 3, as well as the voltage-dependentresistance 1. The various spark gaps 2 are formed during the stacking oftwo insulating plates 5 from the lower electrode of the upper plate andthe upper electrode of the lower plate. When stacking completelyidentical plates 5, the latter are turned each by 90 so that the twoelectrodes 24 forming a spark gap form an angle of 90. In this way anarc space is formed between two adjoining plates, which extends overabout 270 and of the plate cross section respectively.

The method of operation of the spark gap is as follows: The electricsurge causes an arc to strike across the spark gap, the spark-over pointbeing located in the center of the insulating plate 5, or a littleoutside thereof in the direction of the arc space. The follow-currentmaintains the arc and produces in the magnet coils a blast field underwhose influence the arc moves to the edge of the arc chamber 14. Themoving arc displaces the gas in the chamber 14 through the opening 20 ofthe lower plate downward and through the opening 21 of the upper plateupward (see FIG. 7). After passing through the openings 20 and '21, thegases flow through the channels 26 to the sparkover points of the upperand lower spark gaps and consolidate them electrically.

In the arrangement according to the invention a pressure equalization isachieved between the spark gap chambers, so thatall arcs traveluniformly. The are blow each other out. There is also the additionaladvantage that, right after the start of the migration of the arc, thecharacteristic field, produced by the screw-like flow of the current inthe electrodes, supports the magnetic fields produced by the blastcoils. In addition, the pressure which is formed by high currentimpulses, is offset by the superposed sparkover distances. Besides, theinductivity is very low during the flow of the discharge current and hasa favorable effect on the residual voltage.

We claim:

1. Spark gap arrangement for surge arresters with voltage-dependentresistors and magnetic blast field, where the spark gap comprises aplurality of axially stacked plates of insulating material, which havean electrode on each side, one electrode of one plate forming a sparkgap with the electrode of the adjoining plate; characterized in that thetwo electrodes which belong to one plate and which extend from the platecenter to the edge, are made of one piece, which is inserted from theside into a slot of the plate and fixed there, the entrance of the slotbeing closed by projections on the circumference of the adjacent platesabove and underneath, and that the plates are provided with gas channelswhich permit the circulation of gas from the arc of a spark gap, throughthe plate behind to the sparkover distance of the spark gap above andunderneath.

2. Spark gap arrangement according to claim 1, characterized in that theplates are stacked, offset by each, so that the arc extends over 270 inthe various chambers formed between adjoining plates.

3. Spark gap arrangement according to claim 1, characterized in that ablast coil is connected in series at each end of the stack of sparkgaps, to which one spark gap each is connected in parallel, saidparallel connected spark gaps being of the same construction as theother spark gaps of the arrester.

4. Spark gap arrangement according to claim 1, characterized in that thestack of spark gaps is surrounded by a blast coil which is connected inparallel to one of the spark gaps of the stack.

5. Spark gap arrangement according to claim 1, characterized in that theelectrodes are provided each with a preionizing element which pressesagainst the adjoining insulating plate.

References Cited in the file of this patent UNITED STATES PATENTS

1. SPARK GAP ARRANGEMENT FOR SURGE ARRESTERS WITH VOLTAGE-DEPENDENTRESISTORS AND MAGNETIC BLAST FIELD, WHERE THE SPARK GAP COMPRISES APLURALITY OF AXIALLY STACKED PLATES OF INSULATING MATERIAL, WHICH HAVEAN ELECTRODE ON EACH SIDE, ONE ELECTRODE OF ONE PLATE FORMING A SPARKGAP WITH THE ELECTRODE OF THE ADJOINING PLATE, CHARACTERIZED IN THAT THETWO ELECTRODES WHICH BELONG TO ONE PLATE AND WHICH EXTEND FROM THE PLATECENTER TO THE EDGE, ARE MADE OF ONE PIECE, WHICH IS INSERTED FROM THESIDE INTO A SLOT